The invention relates to an arrangement for indicating the presence of snow and ice accumulations, particularly on road surfaces, railway track structures, and the like.
More specifically, the invention relates to arrangements of that type and comprised of two spaced electrodes separated from each other by an interelectrode gap which is open in downwards direction and further comprised of a circuit which responds to the establishment of a preselected electrical resistance between the two electrodes.
Arrangements of the type in question are operative for generating an indicating signal and/or activating heating devices when an accumulation of snow or ice forms. It is important that these arrangements of capable of detecting all types of freezing precipitation, such as snow, ice, glazed frost, hail, sleet, glazed ice forming around physical objects, frozen fog droplets, and the like.
The known arrangements have the disadvantage that they cannot distinguish between simple rain and other forms of precipitation such as snow crystals, ice, sleet, hail, and also fog which can lead to the formation of frost and glazed ice. The reason for this is that, even in the positive temperature range (above 0.degree. C), precipitation in the form of snow, sleet and hail can occur, so that the thawing and/or indicating arrangement must be designed to be responsive to precipitation in at least the very bottom of the positive temperature range, in addition to of course being responsive to precipitation in the negative temperature range. Evidently, however, in the positive temperature range, precipitation will also and indeed more often take the form of simple rain which, although it does not lead to the formation of ice, nevertheless and undesirably causes the indicating and/or defrosting arrangement to respond. Particularly when the precipitation detection initiates the operation of a heating device, for example for the purpose of melting the freezing precipitation on a surface of a highway or for melting glazed ice covering a railway track switch, the amount of energy expended in the heating operation is quite considerable and accordingly completely unjustifiable if in fact the precipitation which has been detected is merely simple rain.
When the indicating and/or defrosting arrangement is to be used for road pavements, the two electrodes are horizontally spaced apart by an open interelectrode gap whose open side faces downwards. The two electrodes and the interelectrode gap can be considered to be arranged one next to the other in the horizontal direction. As a result, such as electrode arrangement can be built into the road pavement with the upper surface of the electrode arrangement flush with the road surface, so that traffic can travel over the electrode arrangement unimpeded.
However, that electrode arrangement, although advantageous for incorporation into a road pavement, is not particularly suited for use in railway track constructions, because in the latter context the possibility of making the upper surface of the electrode arrangement flush with the surface of the earth is not a requirement and because the expense and trouble involved in such flush installation can be dispensed with without creating any difficulties.
Furthermore, with that electrode arrangement, another problem resides in the fact that the railway track roadbed holds the water resulting from the melting of the freezing precipitation, consequently, if the electrode arrangement is embedded in the track roadbed flush with the upper surface of the roadbed, the water held by the roadbed will surround the precipitation-detecting electrode arrangement; accordingly, it becomes necessary either to somehow lead this water away or else to somehow cause it to evaporate.
Moreover, in the event of snow drift accumulations, there will be a marked tendency for the snow to accumulate alongside the rails of the railway track, due to their elevated position relative to the roadbed and the ties. The aforementioned horizontal disposition of the electrodes of the precipitation-detecting arrangement in no way takes this peculiarity into account.